A conventional overvoltage protector is usually comprised of a pair of elements such as carbon blocks or gas tubes mounted within a housing. Fusible elements, typically discs of solder, are associated with each one of the elements. The arrangement is such that, when an overload condition persists, for example when a power line contacts the telephone line for an extended period of time, the heat generated in the overvoltage element will cause the associated fusible element to melt, thereby establishing a secondary circuit which by-passes the overvoltage element.
More recently the carbon blocks and gas tubes have been replaced by solid state devices. U.S. Pat. Nos. 4,851,956 and 4,939,619 which issued on Jul. 25, 1989, and Jul. 3, 1990, respectively, both to Borkowicz et al. disclose a protector using solid state semiconductor devices, which function as overvoltage protection elements. The two electrodes of each semiconductor protection device are connected between a signal line conductor and a ground of the telephone equipment to be protected, and are under external spring pressure. Each semiconductor protection device fulfils a specific role, both before and after failure, in the circuit where it is a component. Under normal conditions where there is no high voltage or lightning, there is a high impedance between the signal line conductor and the ground through the semiconductor protection device. When an instantaneous high voltage is present between the signal line conductor and the ground terminal, the device turns on and current flows through it to provide an effective short-circuit to ground. If the high voltage ceases without destroying the protection device, it returns to the normal high impedance condition so that the short-circuit will no longer be developed therethrough. However, if an overvoltage surge of high magnitude is present for an extended period of time, the protection device will destructive, and the two electrodes thereof are forced by the associated spiral spring into an electrically conductive relation. Therefore, a conductive short-circuit is created between the signal line conductor and the ground in the circuit through the electrodes of the protection device, and the short-circuit is sustained due to the external pressure of the springs, so that associated telephone equipment is protected from overvoltage/overcurrent. However, these known overvoltage protectors are complicated because of the complexity of the mechanism for applying the external pressure. Alternately, the protector disclosed in U.S. Pat. No. 4,939,619 has cantilever springs which hold the protective devices. However, under the conditions of overcurrent flowing in the springs, they may anneal and loose their elasticity with the result of poor ground contact, thereby leaving the associated equipment unprotected.